Method and system for high-speed precise laser trimming, scan lens system for use therein and electrical device produced thereby

ABSTRACT

A method, system and scan lens system are provided for high-speed, laser-based, precise laser trimming at least one electrical element. The method includes generating a pulsed laser output having one or more laser pulses at a repetition rate. Each laser pulse has a pulse energy, a laser wavelength within a range of laser wavelengths, and a pulse duration. The method further includes selectively irradiating the at least one electrical element with the one or more laser pulses focused into at least one spot having a non-uniform intensity profile along a direction and a spot diameter as small as about 6 microns to about 15 microns so as to cause the one or more laser pulses to selectively remove material from the at least one element and laser trim the at least one element while avoiding substantial microcracking within the at least one element. The wavelength is short enough to produce desired short-wavelength benefits of small spot size, tight tolerance and high absorption, but not so short so as to cause microcracking.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser.No. 60/617,130, filed Oct. 8, 2004, entitled “Laser System And MethodFor Laser Trimming.” This application also claims priority to and is acontinuation-in-part application of U.S. patent application Ser. No.11/131,668, entitled “Method And System For High-Speed PreciseMicromachining An Array Of Devices,” filed May 18, 2005, which is adivisional of Ser. No. 10/397,541, entitled “Method And System ForHigh-Speed Precise Micromachining An Array Of Devices,” filed Mar. 26,2003, which is a continuation-in-part application of U.S. patentapplication Ser. No. 10/108,101, entitled “Methods And Systems ForProcessing A Device, Methods And Systems For Modeling Same And TheDevice,” filed Mar. 27, 2002, now published U.S. patent application No.2002/0162973. U.S. Pat. No. 6,341,029, entitled “Method and Apparatusfor Shaping a Laser-Beam Intensity Profile by Dithering,” assigned tothe assignee of the present invention with a common inventor, is herebyincorporated by reference in its entirety. This application is alsorelated to U.S. Pat. No. 6,339,604, entitled “Pulse Control In LaserSystems,” also assigned to the assignee of the present invention. Thisapplication is also related to U.S. Pat. No. 6,777,645, entitled“High-Speed, Laser-Based Method and System for Processing Material ofOne or More Targets Within a Field” also assigned to the assignee of thepresent invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and systems for high-speed, preciselaser trimming, scan lens systems for use therein and electrical devicesproduced thereby.

2. Background Art

Traditionally, a Nd:YAG laser with wavelength at 1 micron is used fortrimming of chip resistors. As the sizes of resistors get smaller, thesubstrates thinner, and tolerances tighter, this wavelength hits itsfundamental limitations in terms of trimming kerf width, heat affectedzone (i.e., HAZ) and, therefore the drift of TCR and Resistance, R.

It is well known that shorter wavelengths can provide smaller opticalspot size. It is also well known that the absorption of the filmmaterials at shorter wavelength is higher. Therefore, the use of laserswith wavelengths shorter than the traditional 1 micron have theadvantages of smaller kerf width that allows smaller features to betrimmed, and of smaller HAZ that leads to much less TCR drift and Rdrift.

As disclosed in the following U.S. Pat. Nos. 5,087,987; 5,111,325;5,404,247; 5,633,736; 5,835,280; 5,838,355; 5,969,877; 6,031,561;6,294,778; and 6,462,306, those skilled in the art of lens design willappreciate the complexities of scan lenses designed for multiplewavelengths.

Many design parameters are considered and various design trade-offs suchas spot size, field size, scan angle, scan aperture, telecentricity, andworking distance are used to achieve a laser scan lens design solutionfor trimming applications. In order to achieve a small spot over a largescan field, as preferred for high speed processing of fine structuresover large areas, the scan lens must be able to focus a collimated inputbeam and image a diffraction limited laser spot over the entire field.The spot must be sufficiently round and uniform across the field toproduce uniform trim cuts within the field. The lens must also provideadequate viewing resolution to image a selected target area forcalibration and process monitoring. For through-the-lens viewing, lightis collected from the illuminated field, collimated by the scan lens,and imaged onto a detector using auxiliary on-axis optics. By utilizinga different wavelength region for target viewing and an achromatizedscan lens, efficient beam combining and splitting is possible usingconventional dichroic optical elements. Within the viewing channel, goodlateral and axial color correction is required, however small amounts oflateral color between the viewing and laser channels can be accommodatedin the scan system and small amounts of axial color between the viewingand laser channels can be accommodated with focus adjustments in thefield or in auxiliary optics. With a two mirror scan head, for example agalvanometer scan head when pupil correcting optics are not used, thescan lens must accommodate the pupil shift resulting from the separationbetween the two scan mirrors.

Relative lens capability can be determined by dividing the field size bythe imaged spot size to find the number of spots per field. Conventionalachromatized scan lenses for laser trimming, for example, the objectiveused in the GSI Lumonics W670 trim system for thick film trimming with alaser wavelength of 1.064 microns, produces a 30 micron spot over a 100mm square field and images the target with conventional white lightsources and auxiliary camera optics to a monochrome CCD camera. The W670system is capable of about 4667 laser spots over the field diagonal.Lenses in system used for thin film trimming have smaller field sizesand smaller spot sizes. For example, the scan lens used in the GSILumonics W678 trim system, also with white light viewing capability, hasa 12 micron spot over a 50 mm field, or about 4167 spots. Yet anotherthin film scan lens with a laser wavelength of 1.047 microns is used inthe GSI Lumonics M310 wafer trim system, has a 6.5 micron spot over a 1cm sq telecentric field and is capable of about 2175 spots with IR LEDilluminators with an emission band of about 860 nm to 900 nm forviewing.

To some extent, lenses or lens design forms intended for IR laserscanning, especially IR scan lenses with white light viewing, can beused or modified to other laser wavelengths, for example, with greenlasers. Reducing the wavelength theoretically reduces the spot sizeproportionally. However, considering increased lens aberrations andmanufacturing tolerances, this may not be achievable. For example, agreen version of the W670 lens produce a spot of about 20 micronscompared to 30 microns for the IR version, and the number of spots perfield is increased from 4667 to about 7000.

Conversely, it has been found that lenses designed primarily to operateat a green laser wavelength with a viewing channel at a longerwavelength can be optimized to scan a second wavelength, for example1.047 microns or 1.064 microns, producing a spot approximately scaled upby the wavelength.

The following exemplary U.S. Pat. Nos. are related to laser trimmingmethods and systems: 6,534,743; 6,510,605; 6,322,711; 5,796,392;4,901,052; 4,853,671; 4,647,899; 4,511,607; and 4,429,298.

U.S. Pat. No. 4,429,298 relates to many aspects of serpentine trimming.Basically, a serpentine resistor is formed with sequential plunge cutsand a final trim cut is made parallel to the resistor edge from the lastplunge. It describes “progressively” making plunge cuts on a resistoralternately from one end, considers maximum and minimum plunge cutlengths, a resistance threshold of the plunge cuts for the trim cut, afaster cutting speed for plunge cuts, and a structured process flow withvarious resistance and cut length tests.

There is a continuing need for improved high-speed, micromachining suchas precise trimming at all scales of operation, ranging from thick filmcircuits to wafer trimming.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved method andsystem for high-speed, precise laser trimming, scan lens system for usetherein and electrical device produced thereby.

In carrying out the above object and other objects of the presentinvention, a method is provided for high-speed, laser-based, preciselaser trimming at least one electrical element. Each electrical elementhas at least one measurable property and is supported on a substrate.The method includes generating a pulsed laser output having one or morelaser pulses at a repetition rate. Each laser pulse has a pulse energy,a laser wavelength within a range of laser wavelengths, and a pulseduration. The method further includes selectively irradiating the atleast one electrical element with the one or more laser pulses focusedinto at least one spot having a non-uniform intensity profile along adirection and a spot diameter less than about 15 microns so as to causethe one or more laser pulses having the wavelength, energy, pulseduration and the spot diameter to selectively remove material from theat least one element and laser trim the at least one element whileavoiding substantial microcracking within the at least one element. Thewavelength is short enough to produce desired short-wavelength benefitsof small spot size, tight tolerance and high absorption, but not soshort so as to cause microcracking.

The focused pulsed laser output power may correspond to about 10-50 mwwith a spot diameter of less than about 15 μm. The power is scalablewith reduced spot sizes less than about 15 μm such that correspondingpower density is high enough to trim the element but sufficiently low toavoid microcracking.

Any microcracking obtained as a result of removing material from atleast a first portion of the at least one element may be insubstantialcompared to microcracking obtained upon removing material from the atleast one element, or from a portion of a second element, using at leastone other wavelength outside the range of laser wavelengths.

The removal of material from the at least one element may create a trimcut with a kerf width corresponding to the spot diameter.

The step of selectively irradiating with the one or more laser pulsesmay be carried out to at least limit formation of a heat affected zone.

The repetition rate may be at least 10 Kilohertz.

The pulse duration of at least one laser pulse of the laser output maybe in the range of about 25 nanoseconds to 45 nanoseconds.

The pulse duration of at least one laser pulse of the laser output maybe less than about 30 nanoseconds.

An array of thin film electrical elements may be trimmed, and the methodmay further include selectively micromachining one element in the arrayto vary a value of a measurable property. The step of selectivelymicromachining is suspended, and while suspended, at least one otherelement in the array is selectively micromachined to vary a value of ameasurable property. The method may further include resuming thesuspended step of selectively micromachining to vary a measurableproperty of the one element until its value is within a desired range.

The at least one element may include a resistor, and the at least onemeasurable property may be at least one of resistance and temperature.

The method may further include suspending micromachining when ameasurement of the at least one measurable property is within apredetermined range.

Further in carrying out the above object and other objects of thepresent invention, a method of laser trimming at least one electricalelement having a measurable property is provided. The method includesproviding a laser trimmer including a pulsed laser system, a beamdelivery system, and a controller. A control program is provided which,when executed, causes the controller to control the systems to cause oneor more laser output pulses of a pulsed laser output to laser trim theat least one element while avoiding microcracking with the at least oneelement. The pulsed laser output has a repetition rate of about 10 KHzor greater and a visible laser wavelength. The beam delivery system hasan optical subsystem to produce a focused spot having a non-uniformintensity profile along a direction and has a diameter less than about15 microns from the one or more laser output pulses. The wavelength isshort enough to produce the desired short wavelength benefits of smallspot size, tight tolerance and high absorption, but not so short so asto cause microcracking.

The visible laser wavelength may be in a range of about 0.5 microns toabout 0.7 microns.

The diameter may be as small as about 6 microns to about 10 microns.

An array of thin film electrical elements may be trimmed, and the methodmay further include selectively micromachining one element in the arrayto vary a value of a measurable property. The step of selectivelymicromachining is suspended, and while suspended, at least one otherelement in the array is selectively micromachined to vary a value of ameasurable property. The method may further include resuming thesuspended step of selectively micromachining to vary a measurableproperty of the one element until its value is within a desired range.

Further in carrying out the above object and other objects of thepresent invention, an electrical device having at least one thin filmelectrical element trimmed by the method of the invention during atleast one step of producing the device is provided.

Still further in carrying out the above object and other objects of thepresent invention, a system is provided for high-speed, laser-based,precise laser trimming at least one electrical element. Each electricalelement has at least one measurable property and is supported on asubstrate. The system includes a laser subsystem to generate a pulsedlaser output having one or more laser pulses at a repetition rate. Eachlaser pulse has a pulse energy, a visible laser wavelength, and a pulseduration. A beam delivery subsystem accepts the pulsed laser output andincludes at least one beam deflector to position the one or more laserpulses relative to the at least one element to be trimmed, and anoptical subsystem to focus the one or more laser pulses having thevisible laser wavelength into at least one spot within a field of theoptical subsystem. The at least one spot has a non-uniform intensityprofile along a direction and a spot diameter less than about 15microns. A controller is coupled to the beam delivery and lasersubsystems to control the beam delivery and laser subsystems toselectively irradiate the at least one element such that the one or morelaser output pulses having the visible laser wavelength, the pulseduration, the pulse energy and the spot diameter selectively removematerial from the at least one element and laser trim the at least oneelement while avoiding substantial microcracking within the at least oneelement. The laser wavelength is short enough to produce desiredshort-wavelength benefits of small spot size, tight tolerance and highabsorption, but not so short so as to cause microcracking.

The focused pulsed laser output power may correspond to about 10-50 mwwith a spot diameter of less than about 15 μm. The power is scalablewith reduced spot sizes such that corresponding power density is highenough to trim the element but sufficiently low to avoid microcracking.

The spot may be substantially diffraction limited, and the non-uniformintensity profile may be approximately a Gaussian profile along thedirection.

Substantial microcracking may also avoided within material proximal tothe at least one element.

The laser subsystem may include a q-switched, frequency-doubled,diode-pumped, solid state laser.

The laser subsystem may include a q-switched, frequency-doubled, solidstate laser having a fundamental wavelength in the range of about 1.047microns to 1.32 microns, and the visible output wavelength may be afrequency-doubled wavelength in a visible wavelength range of about 0.5microns to about 0.7 microns.

The laser wavelength may be a green laser wavelength.

The green laser wavelength may be about 532 nm.

The spot diameter may be as small as about 6 microns to about 10microns.

The optical subsystem may include a lens that is achromatized at two ormore wavelengths. At least one of the wavelengths may be a visiblewavelength.

The system may further include an illuminator to illuminate a substrateregion with radiant energy at one or more illumination wavelengths. Adetection device may have sensitivity to the radiant energy at one ofthe illumination wavelengths wherein one of the two or more wavelengthsmay be a visible laser wavelength and the other may be the illuminationwavelength.

The optical subsystem may be a telecentric optical subsystem.

The telecentric optical subsystem may include a telecentric lens.

The repetition rate may be at least 10 Kilohertz.

The pulse duration of at least one laser pulse of the laser output maybe in the range of about 25 nanoseconds to about 45 nanoseconds.

The pulse duration of at least one laser pulse of the laser output maybe less than about 30 nanoseconds.

The controller may include means for controlling position of the pulsedlaser output relative to the at least one element.

The controller may include means for controlling the pulse energy toselectively irradiate the at least one element.

The system may further include a substrate positioner to position the atleast one element supported on the substrate relative to and within thefield of the optical subsystem such that the one or more laser pulsesare focused and irradiate the at least one element with a spot diameteras small as about 6 microns to about 15 microns.

The optical subsystem may receive the at least one laser pulsesubsequent to deflection by the at least one beam deflector.

The focused spot diameter may be as small as about 6 microns to about 10microns at any location within the field of the optical subsystem.

The system may further include a calibration algorithm to adjustcoordinates of material to be irradiated within the at least one elementand to thereby precisely control a dimension of a region of materialremoval.

The system may further include a machine vision subsystem including avision algorithm to locate or measure at least one geometric feature ofthe at least one element.

The vision algorithm may include edge detection and the at least onegeometric feature are edges of the at least one element. The edges areused to determine width of the at least one element and to define adimension for material removal.

The at least one element may include a thin-film resistor, and the atleast one measurable property may be at least one of resistance andtemperature. The system may further include means for suspending removalof thin film material of the resistor when a measurement of at least onemeasurable property is within a predetermined range.

A material of the substrate may be a semiconductor, or may be a ceramic.

The at least one element may include a thin-film element.

An array of thin-film electrical elements may be trimmed with thesystem. The controller may include means to selectively micromachine anarray element to vary a value of a measurable property, and means tosuspend the selective micromachining while the selective micromachiningis suspended. The controller may further include means to selectivelymicromachine at least one other array element to vary a value of ameasurable property, and means to resume the selective micromachining tovary a measurable property of the array element until its value iswithin a desired range.

The system may further include a user interface, and a software programcoupled to the interface and the controller. The software program may beadapted to accept pre-trim target values for the at least one elementand to limit an electrical output being applied to the at least oneelement based on the values.

Potential damage to the at least one element may be avoided.

Yet still further in carrying out the above object and other objects ofthe present invention, an achromatized scan lens system for use in alaser-based micromachining system is provided. The laser-basedmicromachining system has a scan field with a laser spot size less than20 microns and a viewing channel with a bandwidth of at least 40 μm. Thescan lens system has multiple lens elements including a doubletcomprising, in succession from a side of an incident micromachininglaser beam: a first element (L₁) having negative optical power, an indexof refraction (n₁) and an Abbe dispersion number (v₁) and a secondelement (L₂) having an index of refraction (n₂) and an Abbe dispersionnumber (v₂), n₁<n₂ and v₁>v₂ to meet the requirements of the spot size,field size and the viewing channel bandwidth.

The doublet may be a cemented doublet having a cemented surface. Thecemented surface may concave away from the incident micromachining laserbeam.

The L₁ may be a plano-concave element. The L₂ may be a bi-convexelement.

L₁ and L₂ may be the second and third elements of the multiple lenselements. The multiple lens elements may comprise at least 6 lenselements.

The above object and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-1 b are schematic views which illustrate current flow linesbefore and after laser trimming, respectively;

FIG. 1 c is a chart which illustrates the effect of various cut types onseveral trim parameters;

FIG. 2 a is a schematic view of an array of chip resistors arranged inrows and columns and which illustrates results using laser trimmingsteps in accordance with an embodiment of the present invention;

FIG. 2 b is a block diagram flow chart further defining trimming stepscorresponding to FIG. 2 a;

FIG. 3 is a block diagram flow chart further defining the trimmingoperations of FIGS. 2 a and 2 b in a system of the present invention;

FIG. 4 a is a schematic view of an array of chip resistors arranged inrows and columns and which illustrates results using laser trimmingsteps in accordance with another embodiment of the present invention;

FIG. 4 b is a block diagram flow chart further defining trimming stepscorresponding to FIG. 4 a;

FIG. 5 is a block diagram flow chart further defining the trimmingoperations of FIGS. 4 a and 4 b in a system of the present invention;

FIG. 6 a is a schematic view of a laser trimming system which may beused in at least one embodiment of the invention;

FIG. 6 b is a schematic view of a resistor which has geometricproperties to be measured, specifically edges of the resistor, usingdata obtained with the system of FIG. 6 a;

FIG. 7 is a graph which shows position of a laser beam versus timeduring scanning of a resistor array in one embodiment wherein a fastscan with a solid state deflector is superimposed with aelectromechanical linear scan to selectively form the cuts of eitherFIG. 2 or FIG. 4 at increased speed;

FIG. 8 is a schematic view of a system delivering multiple focused beamsto at least one resistor so as to increase trimming speed;

FIG. 9 is a schematic view of a system which provides multiple beams toat least one resistor in a laser trimming system;

FIG. 10 is an electron micrograph (reproduced from FIG. 11 of U.S. Pat.No. 6,534,743) of kerf showing microcracks formed in the substrate of aresistor trimmed by a Gaussian beam produced by a UV laser;

FIG. 11 is a view of a thin film resistor processed by a green laser;

FIG. 12 is a view of kerf width 6-7 microns which has been achieved by agreen laser with newly designed optics;

FIG. 13 is a view of a chip resistor trimmed by a green laser; and

FIG. 14 is a 3D layout view of an 8 micron Green/IR scan lens for use inone embodiment of a laser system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

High-Speed Serpentine Trimming Process

In resistor trimming, the cuts direct the current flowing through theresistive material along a resistance path. Fine control and adjustmentof the cut size and shape change the resistance to a desired value, asillustrated in FIGS. 1 a-1 c. Typically, chip resistors are arranged inrows and columns on a substrate. FIG. 2 a shows an arrangement wherein arow of resistors R1, R2, . . . RN is to be processed. A probe array,having a probe 200 and depicted by arrows in FIG. 2 a, is brought intocontact 202 with the conductors of a row of resistors. A matrix switchaddresses the contacts for a first pair of conductors (e.g.: contactsacross R1) and a series of cuts and measurements is performed to changethe resistance between the conductor pair to a desired value. When thetrimming of a resistor is complete. the matrix switches to a second setof contacts at the next row element (e.g.: R2) and the trimming processis repeated. When a complete row of resistors (R1 . . . RN) has beentrimmed, contact is broken between the contacts and the probe array. Thesubstrate is then relatively positioned to another row, the probe arrayis brought into contact, and a second row is processed in the manner asthe preceding row.

The trimming of serpentine thin film resistors, for instance asillustrated in FIG. 1 c, involves laser processing to createinterdigitated cuts in an area of resistive material between conductors.The interdigitated cuts direct current flowing through the resistivematerial along a serpentine path that wraps around the cuts. Thisgeometry allows a wide range of resistances to be created with a singleareal film/conductor layout. The approach outlined above would process asequence of serpentine cuts with measurement steps at a resistor siteand then move to the next resistor.

Referring to FIG. 2 a, an initial laser position for any cut is depictedas 205, and a beam positioner directs the beam along the linear paththrough the resistor material. In accordance with the present invention,a new paradigm trims a leg on a first resistor (e.g. trim cut 204 of R1)and measures the resistance. If the resistance is below a predeterminedthreshold, similar collinear trims across other resistors R2 . . . RN inthe row are made. A completed collinear trim along the row isillustrated at 210 in FIG. 2 a, and the corresponding block 220 isfurther defined in FIG. 2 b. In at least one embodiment of the presentinvention, a subset of resistors may be measured to determine thin filmconsistency across the substrate, but if the thin film is of knownconsistency one measurement may be sufficient.

The next collinear group of cuts along resistors of the row is made inthe same manner as shown at 211 of FIG. 2 a and further defined at block221 of FIG. 2 b, the resistor RN being trimmed initially. The process isrepeated as shown in 212-213 of FIG. 2 a with corresponding furtherdefined at blocks 222-223 of FIG. 2 b. If a measurement shows that athreshold has been crossed, trimming of the row R1 . . . RN proceedswith measurement of each resistor so as to trim to value beforeswitching to the next resistor (depicted as 214 at block 224).

Limiting the number of measurements and maintaining a collinear trimtrajectory both increase trim speed.

The flowchart of FIG. 3 further defines steps, corresponding to FIGS. 2a-2 b, and additional processing steps used in a trimming system (e.g.:indexing and loading).

In at least one embodiment, cutting steps may be carried out based uponpre-determined information. By way of example, for some resistor types,a first series of elements may be cut before resistance is measured, thesequence based on pre-determined parameters of the resistor (e.g.:geometry) and/or known film properties, (e.g: sheet resistance).Similarly, a number of non-measured cuts may be determined in a learnmode at the first resistor (e.g: including at least one measurement, oriterative measurements). In one learn mode, iterative measurements aremade and the number of non-trim cuts is determined based on themeasurements and material properties. In at least one embodiment anumber of the non-measured cuts may be calculated.

For example, four cuts may be made without measurement. Referring toFIG. 4 a, an initial condition 410 is illustrated wherein probes areplaced in contact 202 with the row as in FIG. 2 a. Referring to FIG. 4b, the initial condition is further defined at block 420. By way ofexample, FIGS. 4 a-4 b illustrate an embodiment of the trimming processwherein initially four cuts 411 are made without any measurement. Asshown in FIG. 4 b, block 421 defines a predetermined number of cuts(e.g: four), without measurement, based on at least one pre-trim valueor condition. The scan path for completing four cuts is depicted at 405.Then the first resistor R1 in the row is trimmed at 406 and measured todetermine if the target value is reached. If not, the remainingresistors R2 . . . RN are cut (e.g.: without measurement) as depicted at412, further defined by block 422.

Then the process is repeated, beginning with trimming 407 of RN, andthen cutting of R[N-1] to R1 as shown at 413 and further defined byblock 423. Hence, with each change in direction either R1 or RN istrimmed, and if the target value is not reached the remaining resistorsR2 . . . RN or R[N-1] . . . R1, respectively, are cut. A final stepresults after R1 or RN reaches a target value. Each resistor isconnected and trimmed sequentially, illustrated at 414 and furtherdefined by block 424.

The flowchart of FIG. 5 further defines steps corresponding to FIGS. 4a-4 b, and additional processing steps used in a trimming system (e.g.:which includes the steps of indexing and loading).

In one embodiment, wherein pre-determined information is obtained usingiterative measurements, pre-trim values are provided. The values may bespecified by an operator, process engineer, or otherwise obtained. Thesoftware provides capability for specifying or using the pre-trim targetvalues so that the applied test voltage and/or current is controlled.This feature is useful for avoiding voltages that are high enough todamage the part over the wide range of resistance change associated withserpentine trimming. When using a fast resistor measurement system in anembodiment of the invention, the voltage applied to the resistor formeasurement is decreased for the initial low resistance cut to limitcurrent through and potential damage to the resistor. As subsequent cutsare made and the resistance increases, the measurement voltage isincreased.

The exemplary trim and cut sequences of FIGS. 2 a and 2 b and 4 a and 4b may be modified so as to allow for variations in material propertiesand other process parameters and tolerances.

For example, in at least one embodiment of the present invention,additional steps may be utilized when a measured trim cut reaches thetarget value and length is within a predetermined margin of the maximumallowed cut length. Within the margin, variation in the materialproperties may leave some trim cuts short of the target value andrequire additional cuts.

In a first mode, trim cuts are made sequentially in a row of elementsand the location of elements not reaching the target value are saved.With subsequent trim cuts, the remaining elements at the saved locationsare trimmed to the target value.

In a second mode, based on the length of the first element trimmed tovalue, the cut length is reduced to prevent the target value from beingreached and non-measurement cuts are processed to complete the row.Subsequent trim cuts bring all elements in the row to the target value.

In a third mode, the length of at least one prior cut on an element ismodified to prevent subsequent cuts from falling into the marginalcondition. In at least one embodiment, additional steps may be utilizedwhen the value of a measured trim cut is within a predetermined marginof the target value. Within the margin, variation in the materialproperties may leave some elements beyond the target value using fillnon-measurement cuts.

In a first mode, trim cuts are made sequentially in a row of elementsand the location of elements not reaching the target value are saved.With subsequent trim cuts, the remaining elements at the saved locationsare trimmed to the target value.

In a second mode, based on the value measured in the first element, thecut length is reduced to prevent the target value from being reached andnon-measurement cuts are processed to complete the row. Subsequent trimcuts bring all elements in the row to the target value.

In a third mode, the length of at least one prior cut on an element ismodified to prevent subsequent cuts from falling into the marginalcondition.

Experimental data indicates improvements in throughput by cutting allthe resistors in a row as shown in FIGS. 24, as opposed to theconventional single resistor trim technique. By way of example,approximate results are shown in the table below: 32 RESISTOR ROW, 20CUTS PER RESISTOR Laser Q-Rate (KHz) Single Resistor Trim (Sec) Row Trim(Sec) 5 39 28 10 27 16 20 20 10

The overall trim speed increases with an increasing number of resistorsin a row, fewer measurements, and with reduced time for final (i.e.,fine) trimming.

Further, each resistor has additional time to recover from lasergenerated energy. The sequence of cuts may be determined to managetemperature change in an element (e.g. reduce maximum elementtemperature during cutting). For example, with reference to FIG. 4 a,the sequence 405 may be reversed so that a set of cuts are made startingnear the center of an element and progressing to an end of the elementapproaching the conductor and probe. Other sequences, suitable sequencesmay be used (e.g: any sequence of non-adjacent cuts having advantage forthermal management). Preferably, a second element may be cut prior to anadditional step of measuring.

Range of resistance change for serpentine cuts varies from about 1 orderof magnitude (e.g: 10×), two orders of magnitude typical (100×), and upto about 500× with current materials.

Laser Trimming Systems

In at least one embodiment of the invention a laser trimming system maybe first calibrated using a method as described in “Calibrating LaserTrimming Apparatus”, U.S. Pat. No. 4,918,284. The '284 patent teachescalibrating a laser trimming apparatus by controlling a laser beampositioning mechanism to move a laser beam to a desired nominal laserposition on a substrate region, imprinting a mark (e.g., cutting a line)on a medium to establish an actual laser position, scanning theimprinted mark to detect an actual laser position, and comparing theactual laser position with the desired nominal position. Preferably, thelaser beam operates on one wavelength, and the mark is scanned with adetection device that operates on a different wavelength. The detectiondevice views a field that covers a portion of the overall substrateregion, and determines the position of a mark within the field. The '284patent further teaches determining where a beam position is in relationto a camera field of view.

Other calibration techniques may be used alone or in combination withthe '284 method. For instance, U.S. Pat. No. 6,501,061 “LaserCalibration Apparatus and Method,” discloses a method of determiningscanner coordinates to accurately position a focused laser beam. Thefocused laser beam is scanned over a region of interest (e.g. anaperture) on a work-surface by a laser scanner. The position of thefocused laser beam is detected by a photodetector either atpredetermined intervals of time or space or as the focused laser beamappears through an aperture in the work surface. The detected positionof the focused laser beam is used to generate scanner position versusbeam position data based on the position of the laser scanner at thetime the focused laser beam is detected. The scanner position versusbeam position data can be used to determine the center of the apertureor the scanner position coordinates that correspond with a desiredposition of the focused laser beam.

Subsequent to system calibration, which preferably includes calibrationof numerous other system components, at least one substrate havingdevices to be trimmed is loaded into the trimming station.

Referring to FIG. 6 a, partially incorporated from the '284 patent, animproved laser trimming system may include an infrared laser 602,typically having a wavelength from about 1.047 microns—1.32 micronswhich outputs a laser beam 603 along an optical path 604 to and througha laser beam positioning mechanism 605 to a substrate region 606. Forapplication to trimming of thin film arrays, a preferred wavelength ofabout 0.532 microns may be obtained by doubling the output frequency ofthe IR laser using various techniques known in the art and commerciallyavailable.

The laser beam positioning mechanism 605, preferably includes a pair ofmirrors and attached respective galvanometers 607 and 608 (variousavailable from the assignee of the present invention). The beampositioning mechanism 605 directs the laser beam 603 through a lens 609(which may be telecentric or non-telecentric, and preferablyachromatized at two wavelengths) to a substrate region 606, over afield. The X-Y galvanometer mirror system may provide angular coverageof the entire substrate if sufficient precision is maintained.Otherwise, various positioning mechanisms may be used to providerelative motion between the substrate and the laser beam. For instance,a two-axis precision step and repeat translator illustratedschematically as 617 may be used to position the substrate within thefield of galvanometer based mirror system 607,608 (e.g.: in the X-Yplane). The laser beam positioning mechanism 605 moves the laser beam603 along two perpendicular axes thereby providing two dimensionalpositioning of the laser beam 603, across the substrate region 606. Eachmirror and associated galvanometer 607, 608 moves the beam along itsrespective x or y axis under control of a computer 610. Illuminationdevices 611 which may be halogen lights or light emitting diodes producevisible light to illuminate substrate region 606.

A beam splitter 612 (a partially reflective mirror) is located withinthe optical path 604 to direct light energy reflected back along thepath 604 from the substrate region 606 to a detection device 614. Thedetection device 614 includes a camera 615, which may be a digital CCDcamera (e.g.: color or black/white) and associated frame grabber 616 (ordigital frame buffer provided with the camera), which digitizes thevideo input from the television camera 615 to obtain pixel datarepresenting a two-dimensional image of a portion of the substrateregion 606. The pixel data are stored in a memory of the frame grabber616, or transmitted, for instance, by a high speed link, directly to thecomputer 610 for processing.

The beam positioning subsystem may include other optical components,such as a computer-controlled, optical subsystem for adjusting the laserspot size and/or automatic focusing of the laser spot at a location ofthe substrate.

In applying the invention to thin film trimming of resistor arrays, atleast one thin film array is supported by the substrate. The calibrationdata obtained as above is preferably used in combination with anautomated machine vision algorithm to locate an element (e.g. resistorR1) of the array and measure the location of at least one geometricfeature of an element 620 of FIG. 6 b. For instance, the feature may beone of the horizontal edges 621 (e.g.: an edge parallel to theX-direction), and one of the vertical edges 622 (e.g.: an edge parallelto the Y direction) found by analysis of pixel data in memory using oneof numerous available edge detection algorithms. The edges may includemultiple edge measurements along the entire perimeter of a resistor, asample of the edges, or edges from numerous resistors of the array. Thewidth of the resistor is then determined which may be used to define thecutting length, typically as a predetermined percentage of the width.Preferably, the edge information is obtained automatically and used withcalibration data to control the length of each cut within the row R1 . .. RN, for example. Other measurement algorithms may also be used wheresuitable, for instance image correlation algorithms or blob detectionmethods.

Calibration may be applied at one or more points along the cut. In atleast one embodiment the starting point of at least one cut will becorrected with calibration data.

Preferably, the length and the starting point of a plurality of cuts inFIGS. 2 and 4 will be corrected.

Most preferably, the length and starting point of all cuts in FIGS. 2 aand 4 a will be corrected.

In one embodiment, the first resistor (e.g.: R1 or RN) will becalibrated, and a corresponding correction applied to all resistors(e.g.: R1, . . . , RN) of the row.

Complete automation is preferred. However, a semi-automatic algorithmwith operator intervention may be used, for instance where agalvanometer is positioned so that the array element 620 is in thefield, then the beam is sequentially positioned along the elementinteractively and the intensity profile (or derivative or intensity)observed on a display 630 by an operator.

The use of the calibration information to adjust coordinates within thearray region is valuable for improving the precision of laser beampositioning without throughput degradation. Measurements of resistorwidth and the alignment data is useful for both controlling the lengthof a cut and for correcting deviations from linearity andnon-orthogonality of the array relative to the scanner X,Y coordinatesystem. The use of the calibration data for geometric correction isparticularly well suited for use in laser trimming systems having one ormore linear translation stages.

Geometric correction does not necessarily replace other useful systemdesign features including f-theta lens linearity, fan beam compensationetc. The system tolerance stack-up may generally be used to determinetradeoffs between the number of cut calibration locations based onexpected position error. When fanning out the beam, especially withlarge spacing across many resistors, only one is calibrated and aligned.For instance, when the spacing between resistors is relatively large, asingle cut may be calibrated and aligned. Resulting errors in positionare anticipated at elements, to be mitigated in part with system design,f-theta linearity, fan spread compensation etc. Closely spaced cuts of atransverse fan are expected to have smaller errors compared with on axisfan.

Further Throughput Improvements—Optical Techniques

In at least one embodiment of the present invention the throughput maybe further improved by increasing the effective scan rate using one ormore of the techniques below.

Further increases in processing speed with collinear trims can beaccomplished with faster jumps across trim gaps between the resistors ofa row. One such gap 216 is shown in FIG. 2 a. Referring to FIG. 7, in atleast one embodiment of the invention, a single-axis Acousto-Optic BeamDeflector (AOBD) superimposes a saw tooth linear scan pattern 701 as thegalvanometer scans across the row at a constant velocity 702. Duringtrimming the AOBD scans in retrograde motion 703, and, between trims,provides a fast jump 704 to the next cut. This allows the galvanometerto scan at constant velocity and minimizes the contributions of jumps tothe total process time.

The use of acousto-optic deflectors in combination with galvanometersfor speed improvements is known in the art. For instance, U.S. Pat. No.5,837,962 discloses an improved apparatus for heating, melting,vaporizing, or cutting a workpiece. A two-dimensional acousto-opticdeflector provided about a factor of five improvement in marking speed.

U.S. Pat. No. 6,341,029, which is incorporated by reference in itsentirety, shows in FIG. 5 thereof an embodiment having severalcomponents which may be used in a complete system when practicing thepresent invention in a retrograde mode for increased speed. In the '029patent, acousto-optic deflectors and galvanometers, with an associatedcontroller, are shown for dithering CW beams for laser patterning. Alsosee col. 3, line 47 and col. 4 of the '029 patent for additional detailsregarding system construction.

The arrangement of the '029 patent may be readily adapted, usingavailable techniques, so as to provide modifications of opticalcomponents and scan control profiles so as to practice the retrogradescanning technique of the present invention, preferably with additionalhardware calibration procedures.

In another embodiment of the invention, the collinear trims onserpentine resistors may be accomplished in a parallel fashion withmultiple spots along the row. A fan-out grating or other multi-beamgenerating device is used to create a spot array so that 2 or more spotsare formed and aligned according to the resistor pitch along the row.For example, U.S. Pat. No. 5,521,628 discloses the use of diffractiveoptics to simultaneously mark multiple parts. The multiple beams may belower power beams generated from a more powerful laser source, orcombined beams from multiple sources. The scan system scans the multiplebeams and forms spots through a common scan lens simultaneously acrossmultiple resistors. The trim process is similar to the single spotmethod with two or more cuts in parallel during non-measurement cuttingsteps. When the threshold is reached, the system converts to a singlespot mode to serially trim each resistor to value.

Similarly, the collinear trims on serpentine resistors may beaccomplished in a parallel fashion with multiple spots formed on atarget to make parallel cuts. A fan-out grating or other multi-beamgenerating device is used to create a spot array so that 2 or more spotsare formed, the spots being aligned to an element with predeterminedspacing between cuts. If a predetermined number of cuts are performed(e.g. four as shown in FIG. 4 a) then, in one embodiment, the number ofpasses could be reduced by 50% (e.g.: a single pass in each direction).This embodiment may be most useful if resistor process variations andtolerances are well established. The grating may be in an opticallyswitched path so as to selectively form multiple spots or a single spot.

Published U.S. patent application No. 2002/0162973 describes a methodand system for generating multiple spots for processing semiconductorlinks for memory repair. Various modifications in the lens system anddeflector system may be used to generate multiple spots for use in thepresent invention.

In one embodiment, a single laser pulse is used to trim up to tworesistors at one time (e.g., no, one or two cuts). Referring to FIG. 8,two focused spots 801,802 are formed on two cuts by spatially splittingthe single collimated laser beam 803 into two diverging collimated beams804,805. Fine adjustment of the differential frequency controls spotseparation. The use of acousto-optic devices for spatially splittingbeams in material processing applications is known in the art. Forexample, Japanese patent abstract JP 53152662 shows one arrangement fordrilling microscopic holes using a multi-frequency deflector havingselectable frequencies f1 . . . fN.

A laser 806 of FIG. 8 is pulsed at a predetermined repetition rate. Thelaser beam goes through relay optics 807 that forms an intermediateimage of the laser beam waist into the acoustic optic modulator (AOM)aperture. The AOM 808, which operates in the Bragg regime, preferably isused to controllably generate the two slightly diverging collimatedfirst order diffraction laser beams and control the energy in each beam.The AOM is driven by two frequencies, f1 and f2 where f1=f0+df andf2=f0−df where df is a small percentage of the original RF signalfrequency f0. The angle between the two beams is approximately equal tothe Bragg angle for f0 multiplied by 2(df/f0). The AOM controls theenergy in each of the laser beams by modulating the signal amplitudes oftwo frequency components, f1 and f2, in the RF signal 812 and makingadjustments for beam cross-coupling.

After exiting the AOM 808, the beams go through an optional beamrotation control module 809 to rotate the beam 90 degrees so as toorient the beam in either X or Y. In one embodiment, a prism is used forthis rotation, though many rotation techniques are well known asdescribed in related U.S. patent publication No. 2002/0170898.

Next, the beam goes through a set of optics to position the beam waistand set the beam size to be appropriate for the zoom optics andobjective lens 810. The zoom optics also modify the angle between thetwo beams, therefore the angle between the two beams exiting the AOM 808has to be adjusted depending on the zoom setting to result in thedesired spot separation at the focal plane. Next, the laser beams enterthe objective lens 810 which provides a pair of focused spots 801,802 ontwo resistors. The two spots are separated by a distance that isapproximately equal to the focal length of the lens 810 times the anglebetween the two beams. The retrograde and parallel methods can becombined for collinear trimming on serpentine resistors. For example, abeam is scanned by an AOBD then split into a pair and scanned across thefield. Two adjacent resistors are trimmed simultaneously and the jump isfrom resistor N to resistor N+2 to the next pair or resistors.

Alternatively, or with a two-dimensional deflector, a pair of spots maybe produced in a direction orthogonal to the serpentine scan direction.For instance, with relatively simple control and programming of aone-dimensional AOBD, the deflector may be used (with appropriate outputpower control) to simultaneously produce at least two of the four beamsused for making four cuts as shown in FIG. 4 a. As such, the scan timefor the cuts may be reduced by 50%. As a result of programmabledeflection, the AOBD may be preferred over a fan out grating. Themultiple spots may also be produced during coarse and fine trim asneeded.

FIG. 9 illustrates schematically an exemplary embodiment of an improvedlaser trimming system having a module 901 from FIG. 8 added for eitherretrograde scanning, parallel processing, or a combination thereof. Forexample, a signal 902 from the computer 610 may be used to control theAOBD or other solid state deflector 808 in one or more axes, and thebeam rotation module 809, if provided. The module 901 may include relayoptics 807 and other beam shaping components. Preferably, at least oneAOBD is used so as to provide considerable flexibility and ease of use,for example with a digital RF generator providing the control signal 812from the computer 610.

Furthermore, techniques for forming elongated or elliptical spots can beemployed with this invention to further increase processing speed orquality. Improvements in trimming speed associated with spot shaping aredescribed in co-pending published U.S. patent application No.2002/0170898.

Numerous other design alternatives may be used in at least oneembodiment of the invention for enhancing system performance and ease ofuse. For example, alternatives include but are not limited to thefollowing:

1. The system may provide for computer-controlled spot size and/or focusadjustments. U.S. Pat. No. 6,483,071, assigned to the assignee of thepresent invention, illustrates an optical subsystem providing for bothspot size control and dynamic focus for laser based memory repair.

2. Another alternative is control of beam energy with a variable beamattenuator. The attenuator may be an acousto-optic deflector (ormodulator). Neutral density filters or polarization-based attenuatorsmay be used, whether manually or automatically adjusted. In U.S. Pat.No. 6,518,540 a suitable variable attenuator is shown, by way ofexample, having a rotating half waveplate and a polarization-sensitivebeam splitter.

3. The pulse width may be varied using methods known to those skilled inthe art, with the understanding that the energy of a q-switched laserwill vary with repetition rates, particularly at high repetition rates.For dynamic trimming, wherein a measurement is performed between pulses,it may be preferred to maintain substantially constant pulse energy. Amethod for pulse energy control is disclosed in the 6,339,604 patentwhich reduces the variation in energy at the target as the trimmingspeed is decreased (e.g.: larger pulse temporal spacing), correspondingto periods of precision measurement when the resistance value approachesthe pre-determined target value.

4. In at least one embodiment, a diode-pumped, frequency-doubled, YAGlaser is used to trim the resistor array. The output wavelength of 532nm resulted in low drift, absence of microcracking, and negligible heataffected zone when compared to other wavelengths. A pulse width of about25-45 ns may be preferred, with less than 30 ns typical. The preferredmaximum laser repetition rate will be at least 10 KHz. The pulse width,much less than typical for thick film systems, provides for thin filmmaterial removal at a relatively high repetition rate. Preferably, themaximum available pulse energy at the reduced pulse widths and highrepetition rates will allow for losses associated with the diffractiveoptics (e.g: grating or AOBD) so that multiple spots may be provided.

5. The laser may be focused to an approximate, diffraction-limited, spotsize. The spot size will typically be less than about 30 microns orless, with a preferred spot size less than about 20 microns, and a mostpreferred spot size in the range of about 6-15 microns, for instance,10-15 microns.

6. In the illustrated embodiments of the invention, serpentine cuts areillustrated as a series of parallel interdigitated cuts. However, it isto be understood that application of the present invention is notrestricted to forming parallel cuts. Trimming or micromachining so as toproduce a plurality of non-intersecting cuts with a reduced number ofmeasurements is considered to be within the scope of the invention.

7. Further, embodiments of the invention are not restricted to thin filmresistor measurements, but are applicable to other micromachiningapplications wherein a physical property is measurable. The measurementis not restricted to electrical measurements, but may be temperaturemonitoring (for instance, with an infrared sensor), stress, vibration,or other property.

As described herein, a comparative application study was conducted byusing three types of lasers, i.e., a conventional IR laser 1.064 μm, agreen laser 0.532 μm, and a UV laser 0.355 μm. The results of the studyclearly showed that the green laser gives the same or better resultsthan the UV laser in terms of TCR drift and resistance toleranceachieved. However, the samples processed by UV lasers are easy to havemicrocracking in the cut, like those indicated in FIG. 10.

By way of example, a pulsed laser output of about 30 mW was applied tothe resistor material over a spot size of about 13 microns on thesurface. The wavelength was 0.532 microns. Favorable results,particularly absence of microcracking, were found with the greenwavelength. Laser operation may be carried out in a range of about 10 mwto about 50 mw over the 13 micron spot diameter.

The corresponding power density (in Watts/cm²) is a function of the spotsize, and the laser output power in a pulse may be scaled accordingly asthe spot size is changed. For instance, the laser power (in mW) in apulse may be reduced by 4-times if the spot size is 6 microns.

Though a wavelength of 0.532 microns was demonstrated with favorableresults, other wavelengths may be utilized. However, embodiments of thepresent invention avoid wavelengths so short as to cause substantialmicrocracking.

Kerf width as small as 6 microns has been achieved with newly designoptics, shown in FIG. 12. Typically, a kerf width around 12 microns canhandle chip size down to 0402 and 0201. FIG. 13 shows a 0402 resistorprocessed by a green laser.

Microcracking in cuts by UV lasers can be extended inside the filmcausing R and TCR drifts. It becomes more severe and pronounced in thenewer 0402 and 0201 chip resistors due to thinner substrate used.Microcracking propagates and results in catastrophic failure in thesubstrate. Therefore, it is apparent that when the laser wavelengthbecomes too short, for example, into the UV region, the UV processinghas the disadvantages of microcracking and instability caused by thecracking (i.e., drifts in R and TCR due to the cracking and itspropagation in the film material).

Beam homogenization of a UV beam has been proposed (U.S. Pat. No.6,534,743). According to this patent, it reduces the number ofmicrocracks, but does not completely eliminate microcracking.

In addition, UV lasers are intrinsically less stable due to the need oftwo non-linear crystals rather than one. Therefore, UV lasers are moreexpensive than green lasers. Other disadvantages of UV lasers forresistor trimming include substrate damage and sensitivity to beamprofile, that make the process unstable.

Data shown herein indicates that there is no advantage by using UVlasers in trimming these chip resistors. Green lasers have achieved assmall kerfs and TCR as UV lasers can. Shown in FIG. 11 is the partprocessed by a green laser.

With this new capability of 6 micro kerf, there is no doubt that thegreen laser wavelength is short enough to process any future chipresistors from the optical point of view of small spot size.

Therefore, green lasers with a Gaussian beam shape have every advantageof UV lasers have without the risks associated with UV laser processinglike microcracking and instability.

The preferred wavelength should be just short enough to produce thedesirable benefits of short wavelengths like smaller spot sizes, tighttolerance and high absorption, but not too short to cause microcracking.

Various embodiments of the present invention will also generally avoidsubstantial increases in capital and operating costs, processinstability, complexity and instability. By way of example, suchbenefits of the present invention result from avoidance of UVwavelengths (so short to cause substantial microcracking) and theassociated optical components hardware for 3^(rd) harmonic generation.Further, auxiliary beam shaping optics for producing a uniform spotdistribution are not required when practicing embodiments of the presentinvention.

Therefore, the purpose in one embodiment of this invention is the use ofa green laser for the trimming.

Some features of this embodiment are:

-   -   1. The use of a green laser to laser-trim to achieve the small        spot size and high absorption needed for processing smaller chip        sizes, but to avoid the possibility of generating microcracking        and damage to the substrate.    -   2. The use of newly designed optics for the green wavelength as        a means to materialize the green laser processing capability.        The optics are described in greater detail hereinbelow taken        together with FIG. 14.    -   3. The use of a high precision beam positioning system as a        means to materialize the green laser processing capability.    -   4. The use of a trimming system measuring and testing a        subsystem as a means to materialize the green laser processing        capability.

It is desirable for a thin film hybrid trim system to have a scan fieldencompassing a scan area of about 25 mm×50 mm with a spot size with agreen laser less than 20 microns, preferably the spot size is less than12 microns, most preferably a spot of 8 microns or less with about 7000spots across the field diameter; and have a viewing channel with abandwidth of at least 40 nm, preferably 100 nm, and most preferably >100nm. The viewing channel may be a portion of the white light spectrumabove about 550 nm selected with a band pass or high pass opticalfilter. The viewing channel may be selected by the emission spectrum ofan LED illuminator. It is also desirable for scan lens producing an 8micron green spot at 532 nm across the field to also produce a spot at1.064 microns of about 17 microns across the field.

To meet the requirements of a scan area of 25 mm×50 mm, an 8 micron spota 532 nm, a 17 micron spot at 1.064 nm with a selected viewing channel,the following lens form has been found to be effective.

It is to be understood that elements described as having piano surfacesand may be true planar surfaces, or approximately planar with curvedsurfaces having relatively long radii that do not contribute substantialoptical power.

A multiple element achromatic scan lens comprising in succession from aside of incident light:

-   With n₂<n₃-   And v₂>v₃    Preferred Solution (shown in FIG. 14)-   A first bi-concave element (L1)-   A first cemented doublet including plano-concave and bi-convex    elements (L2, L3), the cemented surface concave away from the    incident light-   A second cemented doublet including plano-concave and bi-convex    elements (L4, L5), the cemented surface concave away from the    incident light-   A first negative meniscus element concave toward the incident light    (L6)-   A first bi-convex element (L7)    Triplet Solution

With the airspace L5/L6 removed to create a triplet:

-   A first bi-concave element (L1)-   A first cemented doublet including plano-concave and bi-convex    elements (L2, L3), the cemented surface concave away from the    incident light-   A first cemented triplet including plano-concave, bi-convex    elements, negative meniscus element (L4, L5, L6), the first cemented    surface concave away from the incident light-   A first bi-convex element (L7)    6 Element Solution

With L5 removed to create a 6 element design:

-   A first bi-concave element (L1)-   A first cemented doublet including plano-concave and bi-convex    elements (L2, L3), the cemented surface concave away from the    incident light-   A first plano-convex element (L4)-   A first negative meniscus element concave toward the incident light    (L6)-   A first bi-convex element (L7)

Preferably L2 is an anomalous dispersion glass, for example KzFSN4 IndexDispersion L1 n₁ > 1.58 v₁ < 40 L2 1.85 > n₂ > 1.5 v₂ < 50 L3 n₃ > 1.58v₃ < 40 L4 n₄ > 1.61 v₄ < 35 L5 1.85 > n₅ > 1.5 v₅ < 40 L6 n₆ > 1.61 v₆< 35 L7 1.85 > n₇ > 1.5 v₇ < 40 Effective focal length 110 mm Entrancepupil diameter 13.8 mm Input beam 1/e² diameter 13.8 mm Back workingdistance 150 mm Cutting Wavelength(s) 532 nm, 1.064 μm Spot size 1/e²diameter at .532 μm, 8 μm Spot size 1/e² diameter at 1.064 μm, 17 μmField angle 15° Field size 25 mm × 50 mm Telecentricity <3° Spotroundness ≧90%Green/IR Scan Lens with Through-the-Lens Viewing

Glass Data: Index Dispersion L1 1.65 33.8 L2 1.61 44.3 anomalous L3 1.8125.4 L4 1.81 25.4 L5 1.69 53.3 L6 1.81 25.4 L7 1.62 56.9

The preferred lens can be made by various optical manufacturing vendorsincluding Special Optics, Inc., according to the following productionspecification:

Lens Prescription or Production Specification Surf Type Radius ThicknessGlass Diameter OBJ STANDARD Infinity Infinity 0 STO STANDARD Infinity 013.8 0 2 COORDBRK — 19.05 — 3 COORDBRK — 18.288 — 4 STANDARD −44.21 5SF2 32 5 STANDARD 110.456 2.452387 38 6 STANDARD Infinity 5 KZFSN4 39 7STANDARD 66.522 0.03 BK7 47 8 STANDARD 66.511 13 SF6 47 9 STANDARD−66.511 11.81475 49 10  STANDARD Infinity 7 SFL6 60 11  STANDARD 72.0230.03 BK7 64 12  STANDARD 72.041 21.5 LAKN13 64 13  STANDARD −58.8011.234915 66 14  STANDARD −60.136 7.50409 SF6 66 15  STANDARD −235.4960.5 70 16  STANDARD 224.044 12.5 SK10 73 17  STANDARD −124.842 151.679574 IMA STANDARD Infinity 56.73353

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A method of high-speed, laser-based, precise laser trimming at leastone electrical element having at least one measurable property, the atleast one element being supported on a substrate, the method comprising:generating a pulsed laser output having one or more laser pulses at arepetition rate, each laser pulse has a pulse energy, a laser wavelengthwithin a range of laser wavelengths, and a pulse duration; andselectively irradiating the at least one electrical element with the oneor more laser pulses focused into at least one spot having a non-uniformintensity profile along a direction and a spot diameter less than about15 microns so as to cause the one or more laser pulses having thewavelength, energy, pulse duration and the spot diameter to selectivelyremove material from the at least one element and laser trim the atleast one element while avoiding substantial microcracking within the atleast one element, the wavelength being short enough to produce desiredshort-wavelength benefits of small spot size, tight tolerance and highabsorption, but not so short so as to cause microcracking.
 2. The methodas claimed in claim 2 wherein focused pulsed laser output powercorresponds to about 10-50 mw with a spot diameter of less than about 15μm, the power being scalable with reduced spot sizes less than about 15μm such that corresponding power density is high enough to trim theelement but sufficiently low to avoid microcracking.
 3. The method asclaimed in claim 1 wherein any microcracking obtained as a result ofremoving material from at least a first portion of the at least oneelement is insubstantial compared to microcracking obtained uponremoving material from the at least one element, or from a portion of asecond element, using at least one other wavelength outside the range oflaser wavelengths.
 4. The method as claimed in claim 1 wherein theremoval of material from the at least one element creates a trim cutwith a kerf width corresponding to the spot diameter.
 5. The method asclaimed in claim 1 wherein the step of selectively irradiating with theone or more laser pulses is carried out to at least limit formation of aheat affected zone.
 6. The method as claimed in claim 1 wherein therepetition rate is at least 10 Kilohertz.
 7. The method as claimed inclaim 1 wherein the pulse duration of at least one laser pulse of thelaser output is in the range of about 25 nanoseconds to 45 nanoseconds.8. The method as claimed in claim 1 wherein the pulse duration of atleast one laser pulse of the laser output is less than about 30nanoseconds.
 9. The method as claimed in claim 1 wherein an array ofthin film electrical elements are trimmed, and wherein the methodfurther comprises: selectively micromachining one element in the arrayto vary a value of a measurable property; and suspending the step ofselectively micromachining, and while the step of selectivelymicromachining is suspended, selectively micromachining at least oneother element in the array to vary a value of a measurable property, themethod further comprising resuming the suspended step of selectivelymicromachining to vary a measurable property of the one element untilits value is within a desired range.
 10. The method as claimed in claim9 wherein the at least one element includes a resistor and wherein theat least one measurable property is at least one of resistance andtemperature.
 11. The method as claimed in claim 9 further comprisingsuspending micromachining when a measurement of the at least onemeasurable property is within a predetermined range.
 12. A method oflaser trimming at least one electrical element having a measurableproperty, the method comprising: providing a laser trimmer including: apulsed laser system, a beam delivery system, and a controller; providinga control program which, when executed, causes the controller to controlthe systems to cause one or more laser output pulses of a pulsed laseroutput to laser trim the at least one element while avoidingmicrocracking with the at least one element, the pulsed laser outputhaving a repetition rate of about 10 KHz or greater and a visible laserwavelength, the beam delivery system having an optical subsystem toproduce a focused spot having a non-uniform intensity profile along adirection and having a diameter less than about 15 microns from the oneor more laser output pulses, the wavelength being short enough toproduce the desired short wavelength benefits of small spot size, tighttolerance and high absorption, but not so short so as to causemicrocracking.
 13. The method as claimed in claim 12 wherein the visiblelaser wavelength is in a range of about 0.5 microns to about 0.7microns.
 14. The method as claimed in claim 12 wherein the diameter isas small as about 6 microns to about 10 microns.
 15. The method asclaimed in claim 12 wherein an array of thin film electrical elementsare trimmed, and the method further comprises: selectivelymicromachining one element in the array to vary a value of a measurableproperty; and suspending the step of selectively micromachining,wherein, while the step of selectively micromachining is suspended,selectively micromachining at least one other element in the array tovary a value of a measurable property, the method further comprisingresuming the suspended step of selectively micromachining to vary ameasurable property of the one element until its value is within adesired range.
 16. An electrical device having at least one thin filmelectrical element trimmed by the method of claim 1 during at least onestep of producing the device.
 17. An electrical device having at leastone thin film electrical element trimmed by the method of claim 12during at least one step of producing the device.
 18. A system forhigh-speed, laser-based, precise laser trimming at least one electricalelement having at least one measurable property, the at least oneelement being supported on a substrate, the system comprising: a lasersubsystem to generate a pulsed laser output having one or more laserpulses at a repetition rate, each laser pulse having a pulse energy; avisible laser wavelength, and a pulse duration; a beam deliverysubsystem that accepts the pulsed laser output and includes: at leastone beam deflector to position the one or more laser pulses relative tothe at least one element to be trimmed; and an optical subsystem tofocus the one or more laser pulses having the visible laser wavelengthinto at least one spot within a field of the optical subsystem; the atleast one spot having a non-uniform intensity profile along a directionand a spot diameter less than about 15 microns; and a controller coupledto the beam delivery and laser subsystems to control the beam deliveryand laser subsystems to selectively irradiate the at least one elementsuch that the one or more laser output pulses having the visible laserwavelength, the pulse duration, the pulse energy and the spot diameterselectively remove material from the at least one element and laser trimthe at least one element while avoiding substantial microcracking withinthe at least one element, the laser wavelength being short enough toproduce desired short-wavelength benefits of small spot size, tighttolerance and high absorption, but not so short so as to causemicrocracking.
 19. The system as claimed in claim 18 wherein focusedpulsed laser output power corresponds to about 10-50 mw with a spotdiameter of less than about 15 μm, the power being scalable with reducedspot sizes less than about 15 μm such that corresponding power densityis high enough to trim the element but sufficiently low to avoidmicrocracking.
 20. The system of claim 18, wherein the spot issubstantially diffraction limited, and wherein the non-uniform intensityprofile is approximately a Gaussian profile along the direction.
 21. Thesystem of claim 18, wherein substantial microcracking is also avoidedwithin material proximal to the at least one element.
 22. The system ofclaim 18, wherein the laser subsystem includes a q-switched,frequency-doubled, diode-pumped, solid state laser.
 23. The system ofclaim 18, wherein the laser subsystem includes a q-switched,frequency-doubled, solid state laser having a fundamental wavelength inthe range of about 1.047 microns to 1.32 microns, and the visible outputwavelength is a frequency-doubled wavelength in a visible wavelengthrange of about 0.5 microns to about 0.7 microns.
 24. The system of claim18, wherein the laser wavelength is a green laser wavelength.
 25. Thesystem of claim 24, wherein the green laser wavelength is about 532 nm.26. The system of claim 18, wherein the spot diameter is as small asabout 6 microns to about 10 microns.
 27. The system of claim 18, whereinthe optical subsystem includes a lens that is achromatized at two ormore wavelengths, at least one of the wavelengths being a visiblewavelength.
 28. The system of claim 27, further comprising: anilluminator to illuminate a substrate region with radiant energy at oneor more illumination wavelengths; and a detection device havingsensitivity to the radiant energy at one of the illumination wavelengthswherein one of the two or more wavelengths is a visible laser wavelengthand the other is the illumination wavelength.
 29. The system of claim18, wherein the optical subsystem is a telecentric optical subsystem.30. The system of claim 29, wherein the telecentric optical subsystemincludes a telecentric lens.
 31. The system of claim 18, wherein therepetition rate is at least 10 Kilohertz.
 32. The system of claim 18,wherein the pulse duration of at least one laser pulse of the laseroutput is in the range of about 25 nanoseconds to about 45 nanoseconds.33. The system of claim 18, wherein the pulse duration of at least onelaser pulse of the laser output is less than about 30 nanoseconds. 34.The system of claim 18, wherein the controller includes means forcontrolling position of the pulsed laser output relative to the at leastone element.
 35. The system of claim 18, wherein the controller includesmeans for controlling the pulse energy to selectively irradiate the atleast one element.
 36. The system of claim 18, further comprising asubstrate positioner to position the at least one element supported onthe substrate relative to and within the field of the optical subsystemsuch that the one or more laser pulses are focused and irradiate the atleast one element with a spot diameter as small as about 6 microns toabout 15 microns.
 37. The system of claim 18, wherein the opticalsubsystem receives the at least one laser pulse subsequent to deflectionby the at least one beam deflector.
 38. The system of claim 36, whereinthe focused spot diameter is as small as about 6 microns to about 10microns at any location within the field of the optical subsystem. 39.The system of claim 18, further comprising a calibration algorithm toadjust coordinates of material to be irradiated within the at least oneelement and to thereby precisely control a dimension of a region ofmaterial removal.
 40. The system of claim 18, further comprising amachine vision subsystem including a vision algorithm to locate ormeasure at least one geometric feature of the at least one element. 41.The system of claim 40, wherein the vision algorithm includes edgedetection and the at least one geometric feature are edges of the atleast one element, the edges being used to determine width of the atleast one element and to define a dimension for material removal. 42.The system of claim 18, wherein the at least one element includes athin-film resistor, and wherein the at least one measurable property isat least one of resistance and temperature, and wherein the systemfurther includes means for suspending removal of thin film material ofthe resistor when a measurement of at least one measurable property iswithin a predetermined range.
 43. The system of claim 18, wherein amaterial of the substrate is a semiconductor.
 44. The system of claim18, wherein a material of the substrate is a ceramic.
 45. The system ofclaim 18, wherein the at least one element includes a thin-film element.46. The system of claim 18, wherein an array of thin-film electricalelements is to be trimmed with the system and wherein the controllerincludes: means to selectively micromachine an array element to vary avalue of a measurable property; means to suspend the selectivemicromachining while the selective micromachining is suspended; means toselectively micromachine at least one other array element to vary avalue of a measurable property; and means to resume the selectivemicromachining to vary a measurable property of the array element untilits value is within a desired range.
 47. The system of claim 18, furthercomprising a user interface, and a software program coupled to theinterface and the controller, the software program adapted to acceptpre-trim target values for the at least one element and to limit anelectrical output being applied to the at least one element based on thevalues.
 48. The system of claim 47, wherein potential damage to the atleast one element is avoided.
 49. An achromatized scan lens system foruse in a laser-based micromachining system having a scan field with alaser spot size less than 20 microns and a viewing channel with abandwidth of at least 40 nm, the scan lens system comprising multiplelens elements including a doublet comprising, in succession from a sideof an incident micromachining laser beam: a first element (L₁) havingnegative optical power, an index of refraction (n₁) and an Abbedispersion number (v₁); and a second element (L₂) having an index ofrefraction (n₂) and an Abbe dispersion number (v₂), wherein n₁<n₂ andv₁>v₂ to meet the requirements of the spot size, field size and theviewing channel bandwidth.
 50. The scan lens system of claim 49, whereinthe doublet is a cemented doublet having a cemented surface, and whereinthe cemented surface is concave away from the incident micromachininglaser beam.
 51. The scan lens system of claim 50, wherein L₁ is aplano-concave element, and wherein L₂ is a-bi-convex element.
 52. Thescan lens system of claim 50, wherein L₁ and L₂ are second and thirdelements of the multiple lens elements and wherein the multiple lenselements comprise at least 6 lens elements.